1. Field of the Invention
This invention relates to an air delivery unit for an endoscope, which delivers air into an organ, such as a stomach.
2. Description of the Related Art
Conventionally, an air delivery unit for an endoscope, which delivers air into a body-cavity of a patient, is known. In the air delivery unit, a compressor for compressing the air and a valve for regulating an amount of the discharge of the air are provided, and further a closed-space, in which the air is stored, is formed.
A pressure in the closed-space is adjusted by operating the compressor and the valve such that the pressure in the closed-space equals a setting pressure set by an operator. After the pressure in the closed-space is adjusted, the air in the closed-space is discharged by opening and shutting the valve. The discharged air is delivered into the organ via a video-scope or an optical fiber-scope, and thus a condition of a diseased portion is confirmed.
In order to measure a pressure value in the closed-space during an adjustment of the pressure, a pressure-sensor and an electric circuit including an amplifier and a comparator are provided in the air delivery unit. When the pressure in the closed-space is detected by the pressure-sensor, a voltage, corresponding to the pressure value in the closed-space, is fed from the pressure-sensor to the amplifier. In the amplifier, the voltage fed from the pressure-sensor is amplified. The amplified voltage is fed to the comparator as an output-voltage and then compared with a voltage corresponding to the setting pressure. A power-supply voltage is applied to the pressure-sensor, the amplifier and the comparator via a converter, respectively, and thus the pressure-sensor, the amplifier and the comparator act.
In general, a maximum output-voltage of the output-voltage never exceeds the power-supply voltage of the amplifier. Herein, an input-voltage, corresponding to the maximum output-voltage, is referred to as a limitation input-voltage. When a voltage exceeding the limitation input-voltage is input from the pressure-sensor to the amplifier, a voltage amplified by a predetermined voltage-gain can not be output to the comparator. On the other hand, as the pressure-sensor is designed such that the pressure in the closed-space is measured as precisely as possible, the range of the input-voltage value, in short, the range of the voltage output from the pressure-sensor is sufficiently broad. Therefore, an input-voltage, exceeding the limitation voltage, is occasionally input to the amplifier. When the input-voltage exceeding the limitation voltage is input to the amplifier, a voltage corresponding to the pressure value measured by the pressure-sensor is not output to the comparator, so that pressure in the closed-space can not be adjusted properly.
To solve this problem, conventionally, the power-supply voltage of the amplifier is lifted to lift a value of the limitation input-value. However, as the power-supply voltage of the amplifier is higher than that of the comparator, an operation of the electric circuit becomes unstable, namely, the reliability of the circuit is degraded. Further, as plural converters are required to be provided in the air delivery unit, the number of components increases.
Therefore, an object of the present invention is to provide an air delivery unit for an endoscope, in which the pressure value in the closed-space can be measured precisely without complicating the construction of the electric circuit.
An air delivery unit for an endoscope comprises a pressure-sensor, a voltage descent processor, an amplifier, an electric power supplier. Further, in the air delivery unit a closed-space is formed, the air delivery unit adjusting a pressure in the closed-space by measuring the pressure and then discharging air in the closed-space. The pressure-sensor outputs a pressure-voltage corresponding to a value of the pressure in said closed-space. The voltage descent processor lowers the pressure-voltage and outputs a lowered pressure-voltage. The amplifier amplifies the lowered pressure-voltage generated by the voltage-descent processor and then outputs an amplified pressure-voltage. The electric power supplier applies a power-supply voltage to the pressure-sensor and the amplifier. The voltage descent processor lowers the pressure-voltage such that a linear relationship between the pressure-voltage output from the pressure-sensor and the amplified pressure-voltage output from the amplifier is maintained.